AVMutableVideoComposition sometimes won't play video - objective-c

Question

I'm using this short snippet to set up my video. For some unknown reason - sometimes the video simply won't show up, while for other video it'll work perfectly.
let videoTrack: AVAssetTrack = asset.tracksWithMediaType(AVMediaTypeVideo)[0]
let composition: AVMutableComposition = AVMutableComposition()
let videoComposition: AVMutableVideoComposition = AVMutableVideoComposition()
var videoSize: CGSize = videoTrack.naturalSize
let isPortrait_: Bool = self.isVideoPortrait(asset)
if isPortrait_ {
NSLog("video is portrait ")
videoSize = CGSizeMake(videoSize.height, videoSize.width)
}
composition.naturalSize = videoSize
videoComposition.renderSize = videoSize
// videoComposition.renderSize = videoTrack.naturalSize; //
videoComposition.frameDuration = CMTimeMake(1, 30)
let compositionVideoTrack = composition.addMutableTrackWithMediaType(AVMediaTypeVideo, preferredTrackID: 1)
let timeRange = videoTrack.timeRange
do {
try compositionVideoTrack.insertTimeRange(timeRange, ofTrack: videoTrack, atTime: kCMTimeZero)
} catch {
print("error")
}
let layerInst = AVMutableVideoCompositionLayerInstruction(assetTrack: videoTrack)
layerInst.setTransform(videoTrack.preferredTransform, atTime: kCMTimeZero)
let inst: AVMutableVideoCompositionInstruction = AVMutableVideoCompositionInstruction()
inst.timeRange = timeRange
inst.layerInstructions = [layerInst]
videoComposition.instructions = [inst]
let playerItem = AVPlayerItem(asset: composition)
playerItem.videoComposition = videoComposition
Tho for some videos, it simply wont show them up.
Any suggestions? Thanks!!

Answer 1

Hello i had a relative similar code hope this helps you figure out your problem
class func MergeVideosSequentially(URLS : [NSURL], callback : (error : ErrorType? , outURL : NSURL?) -> Void){
let composition = AVMutableComposition()
//videoTrack
let videoTrack = composition.addMutableTrackWithMediaType(AVMediaTypeVideo, preferredTrackID: kCMPersistentTrackID_Invalid)
let audioTrack = composition.addMutableTrackWithMediaType(AVMediaTypeAudio, preferredTrackID: kCMPersistentTrackID_Invalid)
var cursorTime = kCMTimeZero
for URL in URLS {
let asset = AVAsset(URL: URL)
let assetVideoTrack = asset.tracksWithMediaType(AVMediaTypeVideo).first! as AVAssetTrack
let assetAudioTrack = asset.tracksWithMediaType(AVMediaTypeAudio).first! as AVAssetTrack
var duration : CMTimeRange? = nil
duration = CMTimeRangeMake(kCMTimeZero, asset.duration)
do {
try videoTrack.insertTimeRange(duration!, ofTrack: assetVideoTrack, atTime: cursorTime)
try audioTrack.insertTimeRange(duration!, ofTrack: assetAudioTrack, atTime: cursorTime)
}catch {
print(error)
}
cursorTime = CMTimeAdd(cursorTime, asset.duration)
}
let directory = NSTemporaryDirectory()
let dateFormatter = NSDateFormatter()
dateFormatter.dateStyle = .LongStyle
dateFormatter.timeStyle = .ShortStyle
let date = dateFormatter.stringFromDate(NSDate())
let savePath = "\(directory)/mergedVideo-\(date).mp4"
let url = NSURL(fileURLWithPath: savePath)
let exporter = AVAssetExportSession(asset: composition, presetName: AVAssetExportPresetHighestQuality)
exporter!.outputURL = url
exporter!.shouldOptimizeForNetworkUse = true
exporter!.outputFileType = AVFileTypeMPEG4
exporter!.exportAsynchronouslyWithCompletionHandler({ () -> Void in
let outputURL = exporter!.outputURL
switch exporter!.status {
case .Completed :
dispatch_async(dispatch_get_main_queue(), { () -> Void in
callback(error: nil, outURL: outputURL)
})
default:
callback(error: CCMovieWriterError.CannotMergeClips, outURL: nil)
}
})
}